Obtenção de nanocelulose por hidrólise ácida e enzimática de fibras de algodão de resíduo de tecido tingido com corante índigo

Abstract

Cellulose nanocrystals are nanomaterials derived from cellulose, which is a renewable and abundant resource in nature. Due to combination of properties such as high mechanical strength and modulus of elasticity, reactive surface and biodegradability, these materials have received great attention for applications ranging from reinforcement in polymeric materials, food packaging, to applications in the pharmaceutical area. The production of nanometric cellulose from cotton fibers has been reported in several works published in the literature. The objective of this research was to study the production of nanocellulose from indigo-dyed cotton fibers from waste fabric, via acid and enzymatic hydrolysis routes. Nanocellulose was obtained with and without pre-treatment for dye removal and the effects of the pre-treatment on the characteristics of the nanocellulose were evaluated. For the acid hydrolysis, two treatment conditions for the isolation of cellulose nanocrystals were evaluated: sulfuric acid concentrations of 55% m / m at 60 C and 65% m/m at 45 C, for 30 and 60 min. For the enzymatic hydrolysis, the influence of enzyme complex type (Trichoderma reesei ATCC 26921 and Aspergillus fumigatus), time (0 to 48h) and enzymatic load (7.5 and 12 FPU) were studied. The suspensions obtained after hydrolysis were characterized by the techniques of zeta potential, atomic force microscopy, transmission electron microscopy, infrared spectrophotometry, X-ray diffraction, thermogravimetric analysis, total reducing sugars and high performance liquid chromatography. The results demonstrated that nanocellulose was obtained from indigo dyed cotton fibers, in both processing routes evaluated: via acid and enzymatic hydrolysis. Microscopy images indicated needle shaped celulose from the acid hydrolysis. For the enzymatic hydrolysis, the images showed the presence of nanocellulose with spherical shape. The acid hydrolysis carried out at 65% at 45 C for 60 min resulted in nanocrystals of smaller length and diameter, both for the pretreated fabric and the fabric without pretreatment. For the enzymatic hydrolysis, the pretreatment did not affect significantly the characteristics of the micro and nanocrystalline structures. The average size of the nanocellulose obtained was in the range of 80 to 230 nm. The results of the enzymatic hydrolysis suggest that the best cellulose to glucose conversions occurred using the enzymatic complex Trichoderma reesei ATCC 26921 with enzymatic load of 12 FPU and hydrolysis time of 48h. In summary, this study demonstrated that cellulose nanocrytals can be obtained from indigo-dyed cotton fibers from waste fabric, without the need for pretreatment for dye removal, and the characteristics of the nanomaterials obtained depend on the hydrolysis process used.